Biblio

Session management is a fundamental component of web applications: despite the apparent simplicity, correctly implementing web sessions is extremely tricky, as witnessed by the large number of existing attacks. This motivated the design of formal methods to rigorously reason about web session security which, however, are not supported at present by suitable automated verification techniques. In this paper we introduce the first security type system that enforces session security on a core model of web applications, focusing in particular on server-side code. We showcase the expressiveness of our type system by analyzing the session management logic of HotCRP, Moodle, and phpMyAdmin, unveiling novel security flaws that have been acknowledged by software developers.

Physical Unclonable Functions (PUFs) are a promising technology to secure low-cost devices. A PUF is a function whose values depend on the physical characteristics of the underlying hardware: the same PUF implemented on two identical integrated circuits will return different values. Thus, a PUF can be used as a unique fingerprint identifying one specific physical device among (apparently) identical copies that run the same firmware on the same hardware. PUFs, however, are tricky to implement, and a number of attacks have been reported in the literature, often due to wrong assumptions about the provided security guarantees and/or the attacker model. In this paper, we present the first mechanized symbolic model for PUFs that allows for precisely reasoning about their security with respect to a variegate set of attackers. We consider mutual authentication protocols based on different kinds of PUFs and model attackers that are able to access PUF values stored on servers, abuse the PUF APIs, model the PUF behavior and exploit error correction data to reproduce the PUF values. We prove security properties and we formally specify the capabilities required by the attacker to break them. Our analysis points out various subtleties, and allows for a systematic comparison between different PUF-based protocols. The mechanized models are easily extensible and can be automatically checked with the Tamarin prover.

Cryptographic APIs are often vulnerable to attacks that compromise sensitive cryptographic keys. In the literature we find many proposals for preventing or mitigating such attacks but they typically require to modify the API or to configure it in a way that might break existing applications. This makes it hard to adopt such proposals, especially because security APIs are often used in highly sensitive settings, such as financial and critical infrastructures, where systems are rarely modified and legacy applications are very common. In this paper we take a different approach. We propose an effective method to monitor existing cryptographic systems in order to detect, and possibly prevent, the leakage of sensitive cryptographic keys. The method collects logs for various devices and cryptographic services and is able to detect, offline, any leakage of sensitive keys, under the assumption that a key fingerprint is provided for each sensitive key. We define key security formally and we prove that the method is sound, complete and efficient. We also show that without key fingerprinting completeness is lost, i.e., some attacks cannot be detected. We discuss possible practical implementations and we develop a proof-of-concept log analysis tool for PKCS\#11 that is able to detect, on a significant fragment of the API, all key-management attacks from the literature.